86 C. D. WalcoU — The Geologist at Blue Mountain. 



that portion of the North American continent tlien above the 

 sea is thought to have consisted of (1) a large part of what is 

 now the British possessions ; (2) a long, broad mountain area 

 (Atlantic) extended southwestward from Newfoundland to the 

 present site of the Gulf of Mexico and it may be the West Indian 

 archipelago, (3) and one or more areas (Pacific) on the Avestern 

 side of the continental plateau, on the line of the present Rocky 

 mountain and Sierra Nevada ranges* The eastern or Atlantic 

 area and the bed of the interior sea toward the west, in what may 

 be called the Appalachian trough, were then formed of variouss 

 kind of rock, including granite, schists of various kinds, crystalline 

 and unaltered sedimentary rocks and, in some localities, of great 

 masses of volcanic material that had been poured out over the 

 surface in very much the same manner as were the relatively 

 recent lavas found in the vicinity of the Yellowstone National 

 Park and in various parts of the Rocky mountain region. 



The waves of the interior sea wore away from the western 

 shore of the Atlantic land area various rock materials and depos- 

 ited them along with that brought in by the brooks and rivers as 

 layers of sand and gravel on the sea-bed all the way from the 

 present site of the Saint Lawrence river to Alabama. In these 

 deposits fragments of the volcanic rocks, schists, etc, were min- 

 gled, and spread out in sheets. At times the supply of ma- 

 terial was very fine and formed thin layers of mud that after- 

 ward consolidated into shales and slates. After a deposition of 

 several thousand feet of this character of materials the water 

 deepened, probably by the subsidence of the bed of the sea, and 

 calcareous muds were deposited during a great interval of time 

 until in places they reached the thickness of several thousand 

 feet. These now form the limestones found in the Cumberland 

 and Shenandoah valleys and their extensions northward to 

 Canada and southward to Alabama. All along this ancient 

 coast line, from Labrador to Alabama, various forms of marine 

 life existed, and their hard parts, such as shells of crustaceans 

 (allied to the living king crab) and other organisms, were buried 

 in the mud and sand. 



The deposition of sediments in the sea, immediately west of 

 tlie Atlantic area, continued until from 12,000 to 40,000 feet in 

 thickness were piled over the ancient sea-bottom, la3^er upon 



* See article on the North American Continent during Cambrian Time, 

 in Twelfth Ann. Rep. U, S, Geol. Survey, 1892, pp. — . 



